1. Field of the Invention
The present invention relates to an ink-jet recording apparatus in which an image with a high quality image can always be formed. The invention can be applied to all equipment that uses recording media such as a sheet, a cloth, a non-woven fabric, or an OHP sheet, e.g., business equipment and mass-production equipment such as a printer, copying machine, or facsimile apparatus.
2. Description of the Related Art
In association with the widespread use of information processing equipment such as a copying machine, a word processor, and a computer and, further, of communication equipment, an ink-jet recording apparatus for recording a digital image by an ink-jet method has rapidly spread as one type of output apparatus for forming (recording) images processed by the information processing equipment or the communication equipment.
A conventional ink-jet recording apparatus comprises a recording head (hereinlater, referred to as a multi-head) which is formed by aligning a plurality of ink discharge nozzles. The nozzles of the recording head discharge ink, and the ink adheres to a recording medium, thereby forming an image. Generally, the ink-jet recording apparatus comprises a plurality of the multi-heads corresponding to colors for the purpose of recording a color image. The conventional ink-jet recording apparatus having the recording heads has excellent characteristics that enables an image with higher quality to be formed or recorded at a higher speed, more quietly, and more inexpensively, as compared with that in accordance with other recording methods.
However, the conventional ink-jet recording apparatus has various problems as described in the following paragraphs numbered (1) to (6).
(1) In the step of producing the recording head, slight differences in the shape of a discharge port of the recording head and in the performance of an electricity-to-heat converter (discharge heater) are produced and, thus, the discharge amounts and the discharging directions of the ink which is discharged from the discharge port are varied. There is a problem (first problem) that unevenness of density occurs in an image and an image quality deteriorates when the discharge amounts and the discharging directions of the ink vary, as mentioned above. A specific example will be described with reference to FIGS. 15A to 15C and FIGS. 16A to 16C. Referring to FIG. 15A, reference numeral 91 denotes a multi-head which comprises eight multi-nozzles 92. Reference numeral 93 denotes ink droplets which are discharged by the multi-nozzles 92 and, ideally, an equal amount of discharged ink should be discharged in the indicated direction as shown in the figure. If the ink is discharged in the aforementioned manner, dots having the same size are shot on a sheet (as shown in FIG. 15B) and an even image having no unevenness of density as a whole can be obtained (as shown in FIG. 15C). However, the discharge amounts and the discharging directions are actually varied depending on the nozzles, so that if printing is executed in the manner similar to the foregoing, the size and the direction of ink droplets which are discharged from the nozzles are varied as shown in FIG. 16A, and dots are shot on a sheet as shown in FIG. 16B. Referring to FIGS. 16A and 16B, there is a blank portion which cyclically satisfies no area factor of 100%, on the contrary, dots are overlapped more than required, and a white streak is caused at the center. The dots which are shot in the above-described state produces a density distribution for the nozzle and the discharged direction shown in FIG. 16C. Consequently, the phenomenon is usually detected as unevenness of density from the eyes of a human.
(2) The amount of discharged ink from one discharge port changes as a function of time, so that there is problem that the unevenness of density occurs in an image and, an image having a proper density cannot be recorded (second problem). Specifically speaking, when an image is scanned in the main scanning direction by the recording head and the image is recorded, energy for driving the discharge accumulates over time and the temperature of the head rises. In accordance therewith, the viscosity of ink decreases and the amount of discharged ink increases. In particular, according to an ink-jet method known as the (hereinafter, bubble jet method, abbreviated to the BJ method) for forming a flying fluid droplet by use of thermal energy and for recording an image, a foaming force increases due to the increase in temperature of the ink and the amount of discharged ink increases remarkably. Consequently, in general, the density of the image is higher on the side of the end of recording in the main scan than that on the side of the start thereof. Although the phenomenon causes a problem for the typical image, a low-density portion at the start of writing may come into contact with a high-density portion at the end of writing, especially in the case of reciprocating recording and thus, the density difference becomes more remarkable. In accordance with the increase in the number of discharge times, a burnt deposit on the heater unit according to the BJ method causes the amount of discharged ink to decrease.
(3) The amount of discharged ink from a discharge port changes because of dirt near the discharge port which is caused by ink mist and sheet powder or dust, the mixture of bubbles and dust within the discharge port, and the thickening by evaporation of an ink solvent, etc. This causes a problem that an image having a proper density cannot be recorded (third problem).
(4) When the phenomenon noted in paragraph (3) occurs is remarkable, that is, the discharge port is clogged and a non-discharge nozzle is caused, there is a problem that a clear white streak appears in the image and the quality of the image degrades. When the appearance of burnt deposit (xe2x80x9ckogaxe2x80x9d) is remarkable according to the BJ recording method, the discharge also becomes defective and the amount of discharged ink excessively decreases, thereby causing the occurrence of the white streak (fourth problem).
(5) There is a possibility of a stoppage of discharge (non-discharge) which is caused by a short circuit due to corrosion, etc. of a power supply line to the nozzles or by a short circuit of a discharge heater in the recording head according to the BJ method. This causes a problem that a clear white streak appears due to the non-discharge and the quality of the image degrades (fifth problem).
(6) If a large part of ink in the ink tank is consumed and there is a small amount of ink remaining in the ink tank, this causes a problem that a patchy portion appears in the whole image and the quality of the image deteriorates (sixth problem).
Conventional ink-jet recording systems cope with the problems (1) to (6) as follows.
Against problem (1), there are methods for recording a test pattern cyclically/non-cyclically, reading it, determining a state of the recording head, and adjusting a method of image processing as disclosed in Japanese Patent Laid-Open No. 57-41965, Japanese Patent Publication No. 2708439, and Japanese Patent Publication No. 2711011. These methods are used when a user sees an image which is usually recorded and determines that the image is degraded. If specific handling which is different from the usual use such as exchanging of the head or exchanging of an ink tank, is required, the adjustment is executed. As mentioned above, all of the nozzles are adjusted so as to eliminate the variations of the amount of discharged ink and the discharging direction of the discharge ports.
Against problems (2) and (3), there is a method for cyclically/non-cyclically wiping and cleaning the discharge ports. The method is performed when a user judges that the image is degraded, the head is exchanged, the ink tank is exchanged, or the head is unused for a predetermined time period. As described above, against problems (2) and (3), all of the nozzles are subjected to recovering processes such as wiping and cleaning so as to properly discharge ink, thereby coping with the change in amount of discharged ink from one discharge port over time and thickening of the ink.
When the discharge of ink stops as in problems (4) and (5), the user visually finds it and copes therewith. In other words, the user judges that the image deteriorates and determines that the exchanging of the head is required.
Against problem (6), there is a method for automatically detecting the remaining ink and notifying the user of the detected result via a host computer, etc., as well as the method for visually judging the image by the user. In this manner, the user can know that the ink supply should be replenished in the ink tank.
Although conventionally, the countermeasures are performed against problems (1) to (6) by the above-described methods, the user must judge the state of the recorded image according to the conventional methods and thus, these methods are troublesome for the user. Currently, a high speed and a large capacity are required for the ink-jet recording apparatuses as office-automation equipment. If the problems (1) to (6) arise, the above-described methods not only are troublesome for the user but also take a long time because the user must determine which the coping method to employ, thus reducing the recording speed. According to the methods, the user must always monitor the recorded image and this imposes a burden upon the user. Particularly, as the amount of recording data increases, the burden increases.
Continuity of operation and high availability are requirements for an ink-jet recording apparatus for industrial applications, e.g., textile and printing. If the head is exchanged with every occurrence of the non-discharge nozzle, the apparatus must be stopped with every exchange of the head and thus, not only the availability of the system decreases, but also the throughput decreases.
In view of the problems associated with these coping methods, a method disclosed in Japanese Patent Publication No. 3-33508 (U.S. Pat. No. 4,328,504) is considered. Japanese Patent Publication No. 3-33508 discloses that a recorded image is read by optical reading means, a nozzle is cleaned when it is detected that no ink dot exists at the place to which the image ought to be recorded, the size of ink dot to be recorded is not correct, and the condition of driving discharge-operation and a scanning speed of the head, etc., are changed if it is detected that the place to which the ink dot is recorded is not correct.
Although, according to the method disclosed in Japanese Patent Publication No. 3-33508, the nozzle is cleaned when the first discharge defect is detected, in other words, it is detected that no ink dot exists at the place to which the ink dot ought be recorded, it is useless to clean the nozzle if the absence of ink in the ink tank causes the first discharge defect. That is, because, even if the nozzle is cleaned, dischargeable ink is not available and the first discharge defect is not solved. In the case of causing the first discharge defect occurring due to a short circuit of the discharge heater, again it cannot be solved by cleaning the nozzle. According to the method disclosed in Japanese Patent Publication No. 3-33508, the useless operation is executed and this wastes time and the throughput further decreases. If the first discharge defect is not solved by cleaning the nozzle and the recording is continued by using the head, a white streak may occur in the image. The apparatus must be halted when exchanging the head, thereby resulting in a decrease in recording speed.
According to the method disclosed in Japanese Patent Publication No. 3-33508, when the second discharge defect is detected, in other words, it is detected that the position at which the ink dot is recorded is not correct, the scanning speed of the head and the discharging speed of the ink are changed. However, it is difficult to ensure the variation in sub-scanning directions of the discharge are corrected by adjusting the two above-mentioned speeds. Also, changing of the two speeds on every detection of a second discharge defect complicates the control operation.
Further, according to the method disclosed in Japanese Patent Publication No. 3-33508, when the third discharge defect is detected, that is, it is detected that the size of the ink dot to be recorded is not correct, a driving condition of the nozzle for discharging ink is changed. However, if the extent of the discharge defect is large, it is insufficient merely to change the driving condition, with the result that the recording is executed in a state in which the correction is insufficient, thus reducing the quality of the image.
Accordingly, as described above, if the method disclosed in Japanese Patent Publication No. 3-33508 is employed, it is impossible to judge precisely an abnormal cause to avoid the waste of time, and to obtain a high quality image having evenness of density.
In order to solve these problems, one object of the present invention is to provide an ink-jet recording apparatus and a recording method capable of precisely determining the cause of deterioration in the quality of image and efficiently overcoming the cause.
Another object of the present invention is to provide an ink-jet recording apparatus and a recording method capable of preventing the decrease in throughput as much as possible and recording an image with a high quality without troubling the user when the discharge defect is caused.
In order to accomplish the objects, according to a first aspect of the present invention, an ink-jet recording apparatus for recording an image by scanning a head having a plurality of ink discharge nozzles and recording the image to a recording medium includes a reading unit for reading the recorded image which is recorded to the recording medium, and a discriminating unit for discriminating whether there is a discharge-defective nozzle or not by detecting a difference of density information between read density-information which is read by the reading unit and image density information to be inherently recorded, wherein when the discriminating unit determines that there is the discharge-defective nozzle, a processing method to be executed is determined from a plurality of processing methods to prevent the deterioration in image due to the discharge-defective nozzle in accordance with a fact that the difference between both the density information is equal to a predetermined value or more.
According to a second aspect of the present invention, an ink-jet recording system for recording an image by a scanning a head having a plurality of ink discharge nozzles to a recording medium includes a reading unit for reading the recorded image which is recorded to the recording medium, a first discriminating unit for discriminating whether there is a discharge-defective nozzle or not by detecting a difference of density information between read density-information which is read by the reading unit and image density information to be inherently recorded every nozzle, a second discriminating unit for discriminating whether the difference between both the density information is equal or more to a predetermined value, or less, and a third discriminating unit for discriminating the number of nozzles in which the difference between both the density information occurs, wherein when the first discriminating unit determines that there is the discharge-defective nozzle, on the basis of the determined result by the second discriminating unit and the third discriminating unit, a processing method to be executed is determined from a plurality of processing methods to prevent the deterioration in image due to the discharge-defective nozzle.
According to a third aspect of the present invention, an ink-jet recording system for recording an image by the scanning a head having a plurality of ink discharge nozzles and recording the image to a recording medium includes a discriminating unit for discriminating whether there is a discharge-defective nozzle every nozzle or not, wherein when the discriminating unit determines that there is the discharge-defective nozzle, a processing method to be executed is determined from a plurality of processing methods to prevent the deterioration in image due to the discharge-defective nozzle in accordance with an information difference between information which is indicated by a normal nozzle and information which is indicated by the discharge-defective nozzle.
According to a fourth aspect of the present invention, an ink-jet recording method for recording an image by scanning a head having a plurality of ink discharge nozzles and recording the image to a recording medium includes a reading step of reading the recorded image which is recorded to the recording medium, a discriminating step of discriminating whether or not there is a discharge-defective nozzle by detecting a difference of density information between read density-information which is read in the reading step and image density information to be inherently recorded, and a determining step of, when it is determined in the discriminating step that there is the discharge-defective nozzle, determining a processing method to be executed from a plurality of processing methods to prevent the deterioration in image due to the discharge-defective nozzle in accordance with a fact that the difference between both the density information is equal to a predetermined value or more.
According to a fifth aspect of the present invention, an ink-jet recording method for recording an image by scanning a head having a plurality of ink discharge nozzles and recording the image to a recording medium includes a reading step of reading the recorded image which is recorded in the recording medium, a first discriminating step of discriminating whether or not there is a discharge-defective nozzle by detecting a difference of density information between read density-information which is read in the reading step and image density information to be inherently recorded, a second discriminating step of discriminating whether or not the difference between both the density information is equal to a predetermined value or more, a third discriminating step of discriminating the number of nozzles in which the difference between both the density information occurs, and a determining step of, when it is determined in the first discriminating step that there is the discharge-defective nozzle, determining a processing method to be executed from a plurality of processing methods to prevent the deterioration in image due to the discharge-defective nozzle, on the basis of the determined result in the second discriminating step and the third discriminating step.
According to a sixth aspect of the present invention, an ink-jet recording method for recording an image by scanning a head having a plurality of ink discharge nozzles and recording the image to a recording medium includes a discriminating step of discriminating whether or not there is a discharge-defective nozzle every nozzle, and a determining step of, when it is determined in the discriminating step that there is the discharge-defective nozzle, determining a processing method to be executed from a plurality of processing methods to prevent the deterioration in image due to the discharge-defective nozzle in accordance with an information difference between information which is indicated by a normal nozzle and information which is indicated by the discharge-defective nozzle.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.